The same United Kingdom where Russia denies the assassination of a former agent with a deadly nerve agent? And you give Pravda credibility in this claim? Sure....
The only entity with which any credibility can be assigned is the OPCW, who arrives today.
And even they are not perfectly credible.
And, of course, any US sources.
Currently, it appears there are no US sources. Clandestine or otherwise.
The “deadly nerve agent” was so deadly, the primary victims went for a nice dinner after they were exposed, and they have recovered?